Helicobacter pylori is a pathogenic bacterium discovered in 1983 and is called a background pathogenic factor of peptic ulcers (such as gastric ulcer and duodenal ulcer), inflammations (such as gastritis), diseases of upper digestive tracts such as gastric cancer, MALT (mucosa-associated lymphoid tissue) lymphoma, or chronic heart disease. At present, studies on the therapy of Helicobacter pylori infectious diseases are being actively made. As the therapy, there are many reports for the purposes of bacterial elimination and prevention of recurrence, as described below. For example, there is numerated administration of a single drug of, e.g., bismuth, antibiotic, proton pump inhibitor (PPI), or anti-ulcer agent, or polypharmacy (such as two-drug therapy and three-drug therapy) comprising a combination of the foregoing drugs (see Internal Medicine, Special Issue, Vol. 78 (1), 1996, by Nankodo). However, these therapies still involve many problems to be solved, such as high frequency of administration of the drug(s), necessity of administration of a lager amount of the drug(s) than the regular dose, crisis of diarrhea or constipation by administration of the drug(s), and generation of resistant bacteria.
As an anti-helicobacter pylori agent, EP811613 discloses derivatives of 4-oxo-1,4-dihydroquinoline or naphthyridine in terms of the following general formula. In the general formula, the substituent (R2 group) at the 2-position of the ring is a C1 to C10 alkyl group, a (C1 to C10 alkyl)phenyl group, a C2 to C10 alkenyl group, a (C2 to C10 alkenyl)phenyl group, a C2 to C10 alkynyl group, a (C2 to C10 alkynyl)phenyl group, a phenyl group, a naphthyl group, a furyl group, a thiophenyl group, or a pyridyl group.

Further, JP-A-10-132784 discloses the following. 3-methyl-4-oxo-1,4-dihydroquinone derivative as an anti-helicobacter pylori agent, in which, however, the substituent at the 2-position is a nonenyl group.

However, creation of a compound having a stronger anti-helicobacter pylori action by single and oral administration is being demanded.
On the other hand, as derivatives of a 3-alkyl-4-oxo-1,4-dihydroquinoline-2-carboxylic acid, in DE1913466, Pol. J. Pharmacol. Pharm., 33(5), 539–544, 1981, Indian. J. Pharm., 39(1), 13–15, 1977, J. Indian Chemical Society, 50(3), 217–218, 1973, and J. Indian Chemical Society, 51(11), 967–969, 1974, there are disclosed compounds having an ethoxycarbonyl group or a (substituted or unsubstituted) NH2—NH—CO— group at the 2-position of the quinoline ring. However, any of these compounds are merely a synthesis intermediate or are merely reported that they have an anti-amoeba activity. These documents neither disclose nor suggest their anti-helicobacter pylori activity.